It has been practiced in the art to transmit stream data such as audio data or the like between devices that are connected on interfaces according to the IEEE1394 standards.
For example, a disk reproducing device and an audio amplifier device will be considered below. Audio data are reproduced from a disk by the disk playback device and send via an IEEE1394 bus. The audio data are received by the audio amplifier device, which performs signal processing on the received audio data and reproduces and outputs the audio data.
At present, audio data are available in various types (data formats). Particularly, devices such as disk reproducing device or the like are designed so as to be compatible with many disks including CD (Compact Disc), MD (Mini Disc), DVD (Digital Versatile Disc), SACD (Super Audio Disc), etc.
A signal format for digital audio stream data in 2 channels R, L, such as on CDs and MDs, is called IEC60958.
A signal format for stream data on DVDs is called multibit linear audio.
A signal format for stream data on SACDs is called 1-bit digital audio (DSD: Direct Stream Digital).
1-bit digital audio data have been developed as higher-quality data than audio data on ordinary CDs, and include 1-bit data that have been ΔΣ-modulated using a very high sampling frequency of 2.842 MHz which 16 times the sampling frequency of 44.1 kHz for the CD format, for example. The 1-bit digital audio data have a frequency range from DC to 100 kHz and a dynamic range of 120 (dB) for the full audio band.
Though various other data formats are also present, the data in the above signal formats will be referred to as “IEC60958 data”, “DVD data”, and “SACD data”.
For signals in the various signal formats for use on various media, there have been established Enhancement to Audio Music Data Transmission Protocol 2.0 (hereinafter referred to as AM824) standards for sending and receiving music data between interfaces according to the IEEE1394 standards. Depending on the various data formats, music data are packetized and transmitted over an IEEE1394 bus.
However, a device for receiving stream data transmitted over the IEEE1394 bus has no means for recognizing the format (data type) of the transmitted stream data, and hence is unable to know the format of the data unless it sees the contents of the data that have actually been received.
If the contents of the received data are actually checked, then a time is naturally required to check the data. When the received data are reproduced and outputted, therefore, the reproduced data may be interrupted in sound or interrupted at starting ends.
The above problem will be described below with reference to FIG. 8 of the accompanying drawings. FIG. 8 schematically shows the manner in which the receiving device operates. In FIG. 8, the received data include stream data that are packetized and sent from the originating device.
For the transmission over the IEEE1394 bus, invalid data streams are placed before and after the actual data stream. Ancillary no data represent such invalid data.
In FIG. 8, IEC60958 data are received as the received data up to time t1. Since ancillary no data each having a time length of about 10 msec., for example, are placed before and after the IEC60958 data, ancillary no data between times t1 and t2 in FIG. 8 are invalid data added to the trailing end of the IEC60958 data as real data. The ancillary no data are of an IEC60958 format.
After time t3, SACD data are received. Ancillary no data as invalid data are added before and after the SACD data as real data. Therefore, ancillary no data between times t2 and t3 in FIG. 8 are invalid data added to the leading end of the SACD data.
An IEEE1394 controller, an IEEE1394 interface (IEEE1394I/F), and a signal processor shown in FIG. 8 represent respective circuit portions in the receiving device.
The IEEE1394 interface serves as a receiver for receiving data from the IEEE1394 bus. The signal processor is a circuit portion for processing a signal received by the IEEE1394 interface and reproducing and outputting the processed signal. For example, the signal processed by the signal processor is outputted as sound from a speaker. The contents of the reproduced output are shown in a lowermost section in FIG. 8.
The IEEE1394 controller is a controller for controlling the IEEE1394 interface and the signal processor.
In FIG. 8, data in the IEC60958 format are received up to the time t2. The IEEE1394 interface and the signal processor are in a reception setting corresponding to the IEC60958 format.
Thereafter, the signal type (format) of received stream data is changed at time t2.
However, only the detection of ancillary no data is not enough to determine the format of next real data because it is not possible to determine whether the received ancillary no data are invalid data added before real data or invalid data added after real data.
Consequently, the reception setting of the IEEE1394 interface and the signal processor cannot be changed until time t3.
When SACD data are received as real data at time t3, the IEEE1394 controller confirms the contents of the data and recognizes that the signal type of the received stream data represents SACD data.
Based on the detection of the stream change, the reception setting of the IEEE1394 interface is changed to a reception setting corresponding to the SACD format, and the reception setting of the signal processor is also changed to a reception setting corresponding to the SACD format.
At the time the stream change is detected, the IEEE1394 controller controls the signal processor to operate in a mute mode, preventing the speaker from outputting noise.
After the reception setting of the IEEE1394 interface and the signal processor has been changed, the IEEE1394 controller controls the signal processor to cancel the mute mode. From this time on, the speaker outputs reproduced SACD sound.
It will be seen that after the actual SACD stream data are received, a period of time Tc needs to be consumed until the speaker outputs reproduced sound. The period of time Tc mainly serves as a period of time for changing the reception setting of the signal processor.
During the period of time Tc, the received SACD data are not reproduced and outputted, i.e., music data are interrupted at a starting end.